Abstract
The plant-pathogenic virus, tomato spotted wilt virus (TSWV), encodes a structural glycoprotein (GN) that, like with other bunyavirus/vector interactions, serves a role in viral attachment and possibly entry into arthropod vector host cells. It is well documented that Frankliniella occidentalis is one of seven competent thrips vectors of TSWV transmission to plant hosts, however, the insect molecules that interact with viral proteins, such as GN, during infection and dissemination in thrips vector tissues are unknown. The goals of this project were to identify TSWV-interacting proteins (TIPs) that interact directly with TSWV GN and other structural proteins and to localize expression of these proteins in relation to virus in thrips tissues of principle importance along the route of dissemination. We report here the identification of six TIPs from first instar larvae (L1), the most acquisition-efficient developmental stage of the thrips vector. The TIPs were annotated and confirmed to interact with TSWV proteins, including GN and the nucleocapsid (N) protein. Sequence analyses of these TIPs revealed homology to proteins associated with the infection cycle of other vector-borne viruses. Immunolocalization of the TIPs in L1s revealed robust expression in the midgut and salivary glands of F. occidentalis, the tissues most important during virus infection, replication and plant-inoculation. One of the TIPs, an endocuticular structural glycoprotein that bound GN, co-localized with TSWV at the anterior region of the L1 midgut by 24 hours after ingestion of virus-infected plant tissue. These novel discoveries are essential for better understanding the interaction between persistent propagative plant viruses and their vectors, as well as for developing new strategies of insect pest management and virus resistance in plants.
Author Summary Arthropod vectors play an essential role in the dissemination of viruses that cause diseases in humans, animals, and plants. More than 70% of viruses infecting plants and 40% of viruses infecting mammals are transmitted from one host to another by arthropod vectors. For negative-sense RNA viruses, the arthropod serves as a host as well by supporting virus replication in specific tissues and organs of the vector. The goal of this work was to identify vector/host proteins that bind directly to viral structural proteins and thus may play a role in the infection cycle in the insect. Using the model plant bunyavirus, tomato spotted wilt virus (TSWV), and the most efficient thrips vector, we identified and validated six TSWV-interacting proteins from Frankliniella occidentals first instar larvae. One protein, an endocuticle structural glycoprotein, was able to interact directly with the TSWV attachment protein, GN. These proteins co-localized in infected insect cells, and we found a unique region of the thrips protein that bind to GN. The TSWV-interacting proteins provide new targets for disrupting the virus-vector interaction and could be putative determinants of vector competence.